Prof Patrick Roche

Abstract:

Spectra at 8-13 micron of 10 Seyfert galaxy nuclei, roughly equally divided between types 1 and 2 and the quasar 3C 273, are presented. These sources show no evidence for dust emission features, with the exception of the type 2 Seyfert NGC 7582, which does show the narrow dust emission features at 8.65 and 11.25 micron. Two of the other type 2 Seyferts, NGC 1068 and 5506, have minima near 10 micron, attributed to absorption by cold silicate dust. The remainder have smooth featureless spectra well fit by power laws. The lack of dust emission features is in remarkable contrast to nonactive galaxy nuclei and luminous Galactic H II regions. If dust emission is responsible for the radiation from Seyfert nuclei and from 3C 273, silicate grains are absent or are too cold to radiate significantly below 13 micron while any infrared featureless grains are required to radiate strongly and must exist over a wide range of temperatures.

Abstract:

Spectra at 8 - 13 μm of five spiral galaxies with giant H II regions in their nuclei are presented. The spectra are remarkably similar in showing the [Ne II] 12.81 μm fine structure line accompanied by strong emission features at 8.65 and 11.25 μm. The latter features are commonly associated with solid state transitions on dust grains, and thus provide direct evidence that dust emission dominates the infrared radiation of these objects. The spectra of all five galaxies show a minimum near 10 μm, which in several cases probably contains a contribution from silicate absorption. Extinction values calculated from optical and infrared emission lines ratioed against Hβ indicate only moderate reddening (A$_v$ = 0 - 5 mag). In most of the galaxies, this is far less than the extinction derived from the depth of the minimum in the 8 - 13 μm spectra, even after applying a correction for the contributions from the strong emission features.

Abstract:

The results of extensive IUE monitoring of the optical counterpart of the recurrent periodic LMC X-ray transient A0538-66 are presented. Even when the system is not in outburst dramatic spectral variations occur, accompanied by changes in the temperature and surface area of the continuum emitting region. It is shown that, in spite of these variations, the out-of-outburst data are consistent with constant bolometric luminosity. The optical outbursts can be powered solely by reprocessed X-rays. The long-term and orbital behavior of the system is discussed in the light of these results. From an analysis of apparently undisturbed P Cygni profiles, the mass-loss rate of the primary via its stellar wind is determined to be about 4 x 10 to the -9th solar masses/yr. Infrared photometry reveals an excess at H and K which is too large to be explained by free-free emission from this wind alone.

Abstract:

A 10-micron spectrum of periodic Comet Grigg-Skjellerup was obtained on 22 June 1982 with the UCL array spectrometer at the United Kingdom Infrared Telescope, Mauna Kea. No emission feature is obvious in the spectrum. The observed spectrum can be fit equally well by a model of small hot absorbing grains or by a composite model with less than or equal to 30 percent (3sigma) warm, ’dirty’ silicate grains. The latter model is consistent with the silicate abundance in Comet Kohoutek, which did display an emission feature at 10 microns.